Electric valve control circuit



May 9, 1944- A. SCHMIDT, JR, ET AL 2,348,652

ELECTRIC VALVE CONTROL CIRCUITS I Filed Nov. 5, 1941 Figl.

I v l T PHASE 2 l9 Excurmuou SHIFTER v cmcuvr Fig 2.

PHASE PHASE SHIFTER 2- l ifiHlFTER M J Inventors August SchmidQJrT,

. Carl C. Herskihd y WW 5. Their Attorney.

- Patented May 9, 1944 ELECTRIC VALVE CONTROL CIRCUIT August Schmidt, Jr., Nlskayuna, and Carl 0. Hersklnd, Schenectady, N. Y., asslgnors to Generai Electric Company, a corporation 01' New York Application November 5, 1941, Serial No. 417,922

2 Claims.

Our invention relates to electric control circuits and more particularly to control or protective circuits for electric valve translating apparatus.

In accordance with-the teachings of our invention described hereinafter, we provide new and improved control circuits for electric valve translating apparatus of the type employing an ionizable medium and comprising an immersionignitor type control member.

It is an object of our invention to and improved electric valve circuits.

It is another object of our invention to provide new and improved controlcircuits for electric valve translating apparatus of the type employing immersion-ignitor control members.

It is a further object of our invention to provide new and improved protective circuits for electric valve translating apparatus of the type provide new employing immersion-ignitor control members wherein the electric valve means is controlled in response to a predetermined electrical condition, such as arc-back of the electric valves, to render the electric valve means nonconducting, thereby suppressing the arc-back.

Briefly stated, in the illustrated embodiments of our invention we disclose new and. improved arrangements for protecting electric valve means oi the type which employ immersion-ignitor control members wherein the associated excitation circuit or the electric valve means itself is controlled in response to the occurrence of an areback condition to maintain the electric valve means nonconducting for a predetermined interval of time, thereby suppressing the arc-back condition and restoring the system to a condition suitable for normal operation. I

For a better understanding of our invention, reference maybe had to the following description taken in connection with the accompanying drawing, and its scope will be pointed. out in the Referring now to Fig. 1 of the accompanying.

drawing, an embodiment of our inventionis diaphase electric valve converting system, such as a polyphase rectifier, for supplying power to a diappended claims. Fig. 1 diagrammatically illusgrammatically illustrated as applied to a polyrect current load circuit, including a positive com ductor l and a negative conductor 2, from an alternating current supply circuit 3. The translating apparatus comprises an inductive network having a plurality of electrically displaced phase windings which may be provided by means of a transformer 4 having a plurality of primary windings 5 and two groups of electrically displaced phase windings 8, l, 8, and 8, Ni, ii. The secondary windings may be arranged in the conventional double-Y relationship wherein the neutral junctures or the two groups of phase windings are interconnected through a phase equaliz ing or interphase transformer 12 which is connected to the negative terminal 2 of the direct current load circuit. 7

Electric valve means is associated with each of the phase windings 8-H, inclusive, and are connected between the respective phase windings and the positive terminal of the direct current circuit. It is to be understood that electric valve means are associated with each of these windings, but for the purpose of illustrating our invention only electric valve means It and I4 associated with windings 5 and lljare shown. The electric valve means I! and I4 are preferably of the type employing an ionizable medium, such as a gas or a vapor, andeach comprises an anode 8 cathode of the self-reconstructing type such as a mercury pool cathode i6 and an immersionignitor type control member I! which is associated or in contact with the cathode I6. The immersion-ignitor control members H are preferably constructed of a material such as boron carbide or silicon carbide, and which have an electrical resistivity relatively large compared with that of the mercury of the associated pool cathode. The electric valve means l3 and I4 are also provided with auxiliary control means or a control electrode i8 which serves, when properly energized, to accelerate the establishment of arc discharges between the cathodes it and the anodes l5 upon the establishment of cathode spots on. cathodes it due to the proper energization of control members H, The control electrodes it are also constructed and ar ranged sothat if a suitable biasing potential is impressed thereon arc discharges will not be established between cathodes it and anodes it even though the cathode spots have been established on the associated cathodes It by the energization or immerslon-ignitor control members ii. In other words, the-control electrodes l8 serve as means for controlling'the condition of conductivity of the electric valve means I3 and I4.

In order to supply to the immersion-ignitor control members I! impulses of current for establishing arc discharges within the electric valve means I3 and I4 and thereby effecting ionization of the ionizable medium or mercury vapor, we employ an excitation circuit I9 which may be of any of the conventional arrangements now known in the art. The excitation circuit l9 may comprise a plurality of circuits each being of the type disclosed and claimed in U. S. Letters Patent No. 2,110,700 granted March 8, 1938, upon an application of Frank R. Elder and which is assigned to the assignee of the present application. The ex- '1 citation circuit I9, of course, supplies a system of electrically displaced voltages of suitable wave form for energizing the control members II so that the electric valve means associated with windings 6II, inclusive, conduct current in a predetermined order or sequence determined by the order of phase rotation of the system. The excitation circuit I9 is provided with a conductor 20 which is connected to the common cathode connections of the electric valves I3 and I4, and conductors 2I and 22 are connected to the control members ll of electric valve means I3 and I4, respectively. Control members of the other electric valve means (not shown) associated with windings 'I, 8 and 9, I are energized in a corresponding manner from the excitation circuit l9.

We provide a control circuit 23 which supplies to the control electrodes I8 of electric valve means I3 and suitable control voltages which may be periodic or alternating and which have a predetermined phase relationship with respect to the anode-cathode voltages of the associated electric valve means. The excitation circuit 23 comprisesa transformer 24 having a plurality of primary windings 25 and a plurality of' electrically displaced secondary windings 26-3I, in- .clusive. Secondary winding 26 is connected to control electrode I8v of electric valve means I3,

and secondary winding 21 is connected to control electrode I8 of electric valve means I4. Suitable phase shifting means 32 may be employed between the transformer 24 and the alternating current circuit 3 to control or adjust the phase relation of the alternating voltages impressed on control electrodes I8. In this manner the potentials impressed on the control electrodes I8 may be controlled or adjusted to accelerate the establishment of arc discharges between the cathodes I6 and anodes I I5 upon the establishment of cathode spots on the associated cathodes I6 due to the proper energization of immersion-igniter control members I'I. Current limiting resistances 33 and 34 may be connected in series relation with the control electrodes I8 01 electric valve means I3 and I4 respectively.

As a means for impressing on the control electrodes I8 a suitable hold-oil voltage, such as a negative unidirectional biasing voltage, we provide a circuit 35 which may include a suitable impedance element which has aresistance 36 connectedin circuit with the control electrodes I8, and this circuit may include the control means 23 or more particularly the secondary windings of transformer 24. In order to limit the magnitude of the negative biasing potential impressed on control electrodes I8 due to the To impress on the control electrodes I8 a negative unidirectional biasing potential or hold-oil potential in response to a predetermined electrical condition of either the supply circuit or the load circuit, we provide means for shortcircuiting or shunting the resistance 36, thereby efiecting the transmission of an, increased the magnitude of the negative unidirectional biasing potential to a value greater than the above described critical value so that arc discharges will not be propagated from the cathodes I6 to the anodes I5,' even though cathode spots are initiated by the energization of control members I1.

We provide means responsive to an arc-back condition of electric valve means l3. and I4 for effecting application of the negative unidirectional biasing or hold-oil voltage to the control electrodes I8 in response to an arc-back condition or phenomenon of an associated circuit occasioned by arc-back of the electric valve means. For the purpose of illustrating our invention, we employ a polarized current responsive means 39 which is connected to operate in response to the reversal of current flow in the load circuit occasioned by an arc-back of one or more of the electric valve means of the translating system. The current responsive means which is responsive to the direction of current flow comprises an armature 40 which is spring biased to the open circuit position away from contact 4|, a polarized core member 42 and an actuating coil' 43 which may be energized from a shunt 44 connected in the direct current load circuit. When the armature 40 engages contact 4I, resistance 38 is shunted thereby effecting an increase in the magnitude of the biasing or holdoil voltage impressed on control electrodes I8.

The operation 'of the embodiment of our invention shown in Fig. 1 will be explained by considering the system when it is operating as n. polyphase rectifier for supplying current to the direct current load circuit. It will be well understood by those' skilled in the art, that the system operates as a double-three-phase system, the electric valve associated with each winding conducting current during 120 electrical degrees of the supply circuit voltage. The electric valves associated with the two groups of secondary windings'operate in parallel, but each electric valve means in each group conducts current durflow of current through resistance 36 from batv tery 31, we employ a resistance 38 which is con nected in series relation with resistance 36, and

voltages provided by secondary windings 264i, and which are impressed on control electrodes I8, serve to accelerate the transmission of the arc discharges from the cathodes I6 to the anodes I5 upon the proper energization of control members IT. The negative unidirectional biasing potential appearing acrossresistance 36 when re- The phase shifter 32 is adjusted so that the alternating during the cycle of voltage of r 8, we employ a control circuit 6| which impresses trol members H with respect to the applied" anode-cathode voltages.

If an arc-back occurs on one or more of the electric valve means in the translating system,-

there is a reversal of current flow in the direct current circuit including conductors -l and 2.

' Consequently, the current responsive means 39,

transformer 62 which may be energized from the supply circuit3 through a phase shifter 83 so that the time at which the discharge device which is responsive to the direction of current how. will operate effecting engagement of armatune it and contact ll, and thereby effectively short-circuiting resistance 38 to cause the transmission of an increased amount of unidirectional current through resistance 35. The biasing potential which is impressed on control electrodes it under this condition is sumcient to maintain the electric valve means 13 and i4 nonconducting. even though subsequent cathode spots are established on the cathodes it by the energization of control members ll.

Negative unidirectional biasin or hold-oil voltage is impressed on control electrodes I8 so long as the arc-back condition exists, and will be automatically removed by the re-opening of the shunt circuit around resistance 38 when the reverse current condition no longer exists due to the clearance of the iault'or arc-back condition.

Another embodiment of our invention which is illustrated in Fig. 2, is similar in many respects to that shown in Fig. 1, and corresponding elements have been assigned like reference numerals. In the arrangement of Fig. 2 we employ a plurality of excitation circuits for transmitting unidirectional impulses of current to the immersion-ignito'r control members ll of the electric valve means. Only excitation circuit 45 associated with'electric valve means I3 is shown.

This excitation circuit may be energized from the alternating current circuit 3 through a transformer 46 and a phaseshifting device 41. Transformer 46 comprises a plurality of primary windings 48 and secondary windings 49-54 inclusive, Excitation circuit 45 is energized from winding 49. The other secondary windings may be employed as sources of current for energizing the excitation circuits of the electric valves associated with windings 1-4 I, inclusive. The excitation circuit 45 is of the type disclosed and claimed in the above-identified Patent No;

2,110,700 wherein a'capacitance 55 is charged through a unidirectional conducting device 55 and is periodically discharged through an electric discharge device 51 and an inductance 58 to transmit an impulse of unidirectional current to control members ii. If desired, a resistance 59 may also be connected in the discharge circuit for capacitance 55. The electric discharge device 51 is preferably of the type employing an ionizable medium, such as a gas or vapor, and comprises a control grid 50.

In order to control the conductivity oi'the electric discharge device 51 and to render it periodically conducting at predetermined times the supply circuit on the grid 60 a periodic or an alternating voltage. The control circuit 6! may comprise 'a 51 is'rendered conducting may be controlled throughout the cycle of voltage of the supply circuit 3. It will be understood that the second- .bias appearing across resistance 65 and the voltage of the associated secondary winding of transformer t2.

We provide means for increasing the magnitude of the biasing potential impressed on the grid 50 of the electric discharge device 51 in response to a predetermined electrical condition of one of the associated circuits, such as a reverse current condition occasioned by arc-back. This means may comprise a resistance 66 which is connected in series relation with resistance 65 and connected to be short-circuited or shunted by means of contacts 61 of current-relay 39. Upon reversal of power how or current flow discasioned by arc-back, contacts 4| and 5! of the rela 39 are closed substantially simultaneously to effect application of negative or hold-cit voltage to control electrodes l8 and. the grids 60 of electric discharge device 51. In this manner the power electric, valve means are rendered nonconducting and the excitation circuits are prevented from operating so that energizing impulses of current are not transmitted to the immersion-ignitor control members H.

The operation of the embodiment of our invention illustrated in Fig. 2 is substantially the same during normal operation as that set forth above in connection with Fig. 1.

If an arc-back condition occurs, the current directional relay 39 will close its contacts it and 61 by. movement of the armature 40 to chest application of negative or hold-off voltages to control electrodes l8 of power electric valve means l3 and i4, and will also eifectthe application of negative or hold-off voltage to the grid (it of con trol electric discharge device 51. The application of the negative or hold-oil? voltage to the con trol electrodes .IB serves to'suppress the are discharges or arc-backs 0f the electric valve means, and the hold-ofl voltage impressed on grids o1 electricdischarge device 51 prevents operation of excitation circuit 45 so that energizing impulses of current are not transmitted to the im mersion-ignitor control members ll so long as the arc-back condition exists. As soon as the arc-back clears, the spring-biased armature itof relay 89 is moved to the right-hand position indicated in thedrawing and the biasing pctem tials are automaticall removed from control electrode l8 and grid 60. It is, of course, understood that insteadof employing a current responsive relay which automatically opens its control and resets the system, we may employ within the scope of our invention a relay of the type which trips out upon the occurrence of the are period for eiiecting application or the negative or hold-oil. potentials for a predetermined -interval of time, at the expiration of which the biasing potentials are removed to initiate normal operation of the electric valve system.

While we have shown and described our invention as applied to particular systems of connections and as embodying varioiLs devices diagrammatically shown, it will be obvious to those tric valve means and responsive to an arc-back condition of said electric valve means for establishing a low impedance path in parallel with the second-mentioned impedance element to increase the magnitude of the negative voltage impressed on said first-mentioned impedance element.

2. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus interconnecting said circuits and comprising electric valve means including an anode. a cathode, an immersion-ignitor control member in contact with said cathode, and a control electrode, excitation means for transmitting impulses of current to said immersion-ignitor con-j troi member to render said electric valve means conducting periodically and comprising an electric discharge device having a grid, control means connected to said grid for rendering said electric discharge device conducting periodically,

- an impedance element connected in circuit with an immersion-ignitor control member in contact with said cathode, and a control electrode, excitation means for transmitting impulses of current to said immersion-ignitorcontrol members to render said electric valve means conducting periodically, means including a polyphase transformer for impressing an alternating current voltage on said control electrodes, an impedance element connected in circuit between the neutral connection of said polyphase transformer and a common connection between the cathodes of said electric valve means, a source 0! unidirec-' tional voltage and a second impedance element connected in' serie across said first-mentioned impedance element, said source of voltage being poled to produce a voltage on said first-mentioned impedance element tending to render said electric valvemeansnonconductive, and means common to the cathodes of said plurality oi elecsaid control grid and a second impedance element connected in circuit with said control electrode, a source of unidirectional voltage and an' impedance element connected in shunt with each oi said first two mentioned impedance elements,

each said unidirectional voltage source beingso poled as to impress a negative voltage component on said grid and said' control electrode. and means com'mon to the cathodes of said plurality of electric valve means and responsive to an arc-back condition of said electric valve means for establishing a low resistance circuit in shunt with each of said last two mentioned impedance elements to increase the voltage impressed on the impedance elements in circuit with said control electrode and said grid to maintain said valve means nonconducting.

AUGUST SCHIWIDT, JR. CARL C. HERSKIND. 

